In EP 0 974 484 B1 a headrest of this type is described. With this kind of headrest there is the advantage that energy stored by mechanical means, for example, in a stressed spring, can be used to move the head-engaging member toward the back of the head of the passenger, thereby avoiding sharp changes in direction of the head by whiplash in the case of an accident.
EP 0 974 484 B1 describes a mechanical force or energy-storing spring system in which the spring is provided between two members telescopingly fitted one into the other and in which an inadvertent inward movement of the head-engaging member is prevented by a lock preventing backward movement of that member. The device preventing the backward movement comprised two levers acting upon the head-engaging member. This system has the advantage of compact and simple construction.
U.S. Pat. No. 2,973,029 describes a headrest whose cushion carrier is affixed to a ram-like support rod. In the case of a load upon the head-engaging member the headrest and this support bar is displaced into a space in the seat back against the force of a coil compression spring. The support bar has a rachet arrangement of teeth engageable by a pawl so that the headrest can be held in its inwardly displaced position.
The device known from this patent cannot be considered to have a crash-active head support.
U.S. Pat. No. 4,278,291 describes a headrest for a vehicle seat with a movable part in the form of a linear lock with a hand-actuatable locking pin or pawl. A coil compression spring biases the head-engaging member continuously outwardly. If the passenger prefers a particular ergonomic head position, he or she must actuate the pawl and the movable part of the head support. This system as well cannot be deemed to be a crash-active headrest, i.e. one which automatically responds to a crash.
DE 101 38 248 C1 describes a crash-active head support in which the outward movement of the head support member is effected by a transmission. The transmission is combined with a linear directional lock functioning as a back-movement preventer.
DE 200 21 127 U1 (compare FIG. 12) describes a headrest in which the spring-supported outward movement is blocked by two racks which are offset from one another.